Now see if you can apply diffusion to the movement of ions across the membrane
of the axon. In Figure 3 you will find a diagrammatic representation of
the resting state of the axon.
Figure3. A diagram of the axon during the resting potential.
The symbols represent different ions and the relative number of a given
symbol inside and outside of the axon indicates the relative concentration
of that ion inside and outside of the axon. The gaps covered with color
bars are ion channels. The color of the bar represents the type of ion
channel, i.e., the rust bars are sodium channels and the dark green bars
are potassium channels. Click on the figure to see a diagrammatic representation
of the events at the membrane that result from diffusion and the opening
of first sodium and then potassium channels.
As Figure 3 shows, during the resting phase of the axon, the concentration
of sodium is greater outside and the concentration of potassium is greater
on the inside of the axon. Also indicated in Figure 3 are the two most
important ion channels for understanding the action potential, sodium and potassium
channels. Try these questions. See if you can answer them, using the concept of
diffusion only.
Question 1.
If sodium channels were to open, as in Figure 4, what would be the general
direction of flow of the ions through channel and why?
Review
the role that charged ions play in generating the action potential
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contents.